This invention generally relates to a method of concurrently producing at least two structures, each having at least one useful layer on a substrate, for applications in the fields of electronics, optoelectronics or optics. In particular, the method includes providing an initial structure that includes a useful layer having a front face on a support substrate, implanting atomic species to form a zone of weakness within the useful layer, bonding a stiffening substrate is bonded to a front face of the initial structure, and detaching a first useful layer from a second useful layer along the zone of weakness to obtain a pair of semiconductor structures. The first structure includes the stiffening substrate and the first useful layer and the second structure includes the support substrate and the second useful layer.
Several layer transfer methods are known. One concerns implanting atomic species under the surface of a source substrate to create a zone of weakness which delimits a thin layer. The next step is to contact the free face of this thin layer with a support substrate, then to detach the thin layer from the remainder of the source substrate and to transfer it to the support substrate. A description of this type of method can be found in the art with reference to the method known under the registered trademark “SMART-CUT®”. Use of this method results in generating a source substrate remainder that can be recycled and reused during a future layer transfer. However, this process involves polishing and finishing operations that can be long and costly, due to both the cost of the materials used and the time spent on them. In addition, for some extremely hard materials such as silicon carbide, the aforementioned recycling steps can prove to be very long and difficult.
Another known layer transfer method is called “Bond and Etch Back Silicon on Insulator” (“BESOI”). This technique involves a burning-in method and/or chemical etching treatment via chemical attack used after molecular bonding a source substrate to a support substrate. The free surface (or rear face) of this source substrate is then polished until a thin layer of desire thickness is obtained on the support. It is to be noted that such a method destroys the majority of the source substrate as each structure is made, so this technique is not economically viable, especially when the thin layer material is expensive.
Lastly, Silicon on Insulator (“SOI”) type materials include a layer of thick silicon covering a buried layer of silicon dioxide (SiO2) and a transferred superficial layer of silicon, and the same problems concerning recycling exist for the silicon material used to form the transferred layer. In addition to the aforementioned recycling problems, it is difficult to transfer very thin layers, meaning layers that are less than 100 nanometers (100 nm) thick when using the SMART-CUT® type method. Indeed, thin layers transferred in such manner have numerous defects, such as blisters. The defects may be due to, for example, treatments used to strengthen the bonding interface between the thin layer and the support substrate.
The problems concerning transferring very thin good quality layers also exist for SOI substrates. In particular, is noted that the transferred layer of silicon if an SOI structure has defects when less than a certain thickness, for example 20 nm. The defects can increase if a high temperature thermal treatment is also used. In this regard, reference can be made to the article by Q.-Y. Tong, G. Cha, R. Gafiteau and U. Gösele, “Low temperature wafer direct bonding”, J. Microelectomech Syst., 3, 29, (1994).
During thermal treatments, for example to strengthen the bonding interface (which is known as “stabilizing”) after detachment occurs, a gas is created in the bonding interface. In the case of a thick SOI substrate, the transferred layer is thick and fills the role of a stiffener. In the case of a thin SOI substrate in which the transferred layer and/or the oxide layer are thin, the aforementioned absorption and stiffening phenomena do not take place and use of a gas leads to poor bonding.
In addition, as described in published International Application No. WO 01/115218, implantation of atomic species and detachment of the wafer create defects that are principally concentrated on the inside of the layer to be transferred. It has been observed that the thinner the layer the poorer the quality that results.